This invention generally relates to fluorescent lighting systems and particularly to fluorescent lighting systems having low voltage DC power sources such as are found in motor vehicles.
A wide variety of circuits for low voltage fluorescent lighting systems (e.g., 12 volts) have been heretofore used or described in the literature or patents. See, for example, U.S. Pat. No. 4,319,164 (Tulleners), U.S. Pat. No. 4,145,636 (Doli) and U.S. Pat. No. 3,749,977 (Silker). These circuits are designed to convert the current from a low voltage DC power source to an alternating or pulsating current and they include one or more power transistors and transformers. The primary windings of the transformers are usually electrically coupled to the collector of a power transistor and one secondary winding is provided for feedback from the emitter of the power transistor to the base thereof to activate the power transistor. Another secondary winding is provided to generate a high voltage alternating or pulsating current to light the fluorescent lamps. The transformer may also be provided with other secondary windings which are used for preheating one or more of the filaments of the lamp to provide a rapid start thereof.
With the prior art devices, if two fluorescent lamps were to be powered by the same DC source, additional secondary windings would be necessary and no means would be provided to operate the fluorescent lamps independently without complex switching arrangements.
What has been needed and heretofore unavailable is a simple system for the operation of a pair of fluorescent lamps which are powered from the same low voltage DC source but which can be operated together or one of the lamps can be operated independently.